Second Ray: Travels from tip of the object through the optical center of the lens and is not refracted

Draw the real image where rays appear to intersect

First Ray: Travels from tip of the object parallel to principal axis. When it emerges from the lens, it passes through the principal focus

Concave (Diverging)

A lens that is thickest at the ends

Second Ray: Travels from tip of the object through the optical center of the lens and is not refracted

Draw the virtual image where the rays appear to intersect

First Ray: Travels from tip of the object parallel to the principal axis. When it emerges from the lens, it appears to come from the principal focus

Lens Terminology

Principal Focus

The focal point where the light either comes to a focus OR appears to diverge from a focus is given the symbol F, while that on the opposite side of the lens is represented by F'

Focal Length

The distance from the axis of symmetry to the principle to the principal focus measured along the principal axis

Axis of Symmetry

An imaginary vertical line drawn through the optical center of a lens

Optical Center

A point on the axis of a lens that is so located that any ray of light passing through it in passing through the lens suffers no net deviation and that may be within, without, or on the surface of the lens

Principle Axis

An imaginary horizontal line drawn through the optical center perpendicular to both surfaces